This invention is in the general field of nanotechnology and more specifically relates to methods and materials for construction of molecular-scale structures, and devices using the same.
Functional nanostructures that allow investigation into fundamental issues in micromechanics, molecular electronics, statistical physics and the materials science of polar dielectrics are needed. In addition, there is a need in the art for a molecular dipolar rotor which will rotate under application of a force for use in functional devices.
Provided are molecular dipolar rotors comprising: a base; an axle which is attached to the base; and a rotor portion with a dipole moment which is attached to the axle. Preferably, the axle is oriented substantially perpendicularly to the surface. The axle may contain a bearing, which may be a bond, such as a metal-to-xcfx80-face bond. Also provided are surface-mounted molecular dipolar rotors (SMDRs) where the base is attached to a surface and arrays of molecular dipolar rotors attached to a surface.
As used herein, xe2x80x9cbasexe2x80x9d means a structure that is capable of attaching to an axle on one side and to a surface on the other side. Bases may comprise a variety of structures. Bases may include one or more aromatic or nonaromatic rings, for example four, five or six membered ring structures; single atoms such as Si or C; and other structures as known in the art. Preferably, the base is wide to provide resistance to rotational axis tilt (pendulum-type motion). The base is capable of being attached to a surface, through functional groups, preferably spontaneously and covalently. Bases include a variety of structures that perform desired functions, and typically carry atoms that act as leaving groups upon attachment of the base with a surface, such as Cl atoms attached to a Si atom. These functional groups can be attached directly to a base or can be attached through tentacles. Tentacles may be alkyl groups where one or more carbons are optionally substituted with one or more members of the group consisting of: metals; O; S; Si; Oxe2x80x94R (where R is an alkyl group); xe2x80x94Si (OR)3 (where R is an alkyl group); xe2x80x94HgSCOCH3; xe2x80x94HgSCOR (where R is an alkyl group); halogens, ring structures and other structures. Alkyl groups may be short (1 to 5 carbons), medium (5 to 15 carbons) or long (15-25 carbons). The tentacles provide mechanical inertia against tugging by an outside electric field. This can be provided for with massive atoms, for example Hg atoms included in the tentacles. All tentacles on a base do not have to be the same. Preferably the base allows for attachment of more than one tentacle to a surface, however, in some applications, one tentacle attachment to the base or no tentacle attachment to the base through functional groups (i.e., the base is directly attached to the surface) may be desired. Some tentacles may not be used to attach the base to the surface. Some preferred base and tentacle structures are described herein. The particular functional groups used are dependent on a variety of factors, such as the surface the dipolar rotor is bonded to, as known in the art.
Axles may also comprise a variety of structures. For example, an axle may be a triple bond, a single bond, a metal atom such as a transition metal, or may be more complicated, as in Formula 10 where two metal atoms surround a ring. Other axle structures may be used as desired to connect the base to the rotor. The axle should be rigid enough to prevent undesired motions that interfere with the desired operation.
For many purposes it is best if there is a low (less than about 1 kcal/mol) barrier to rotation about the bearing. The barrier to rotation may be higher, as long as the temperature of the system allows the rotor to overcome the barrier. Preferably there are sites on the rotor portion available for substitution, for mechanical balancing. The rotor portion and axle length are preferably a size that prevents the blades from touching the substrate, unless high friction is desired in a particular application. Preferably the rotor portion is about 0.2 to about 5 nm in diameter, depending on the other parameters chosen. A larger rotor portion will maximize the size of the rotating dipole.
The rotor portion is a part of the dipolar rotor that has a dipole moment. It is preferred that the rotor portion have a large dipole moment. A large electric dipole moment is defined as greater than about 5 D, and is preferably greater than 10 D and can be greater than about 20 D. Dipole moments of 1 D or greater are of interest for a variety of applications. The dipole moment of the rotor portion should be sufficient to cause rotation of the rotor portion in an alternating electric field or upon application of another suitable stimulus. It is preferred that the dipole moment be in the plane of the rotor portion. It is preferred that there is a low barrier to rotation of the rotor portion about the axle. This barrier to rotation is preferably less than 1 kcal/mol, but may be higher if sufficient temperature is applied to the rotor. The rotor portion may comprise a ring structure, preferably an aromatic ring, with opposing xe2x80x9cwing tips.xe2x80x9d Preferably the substituents on the wing tips of the rotor portion carry opposite charges, to provide a large dipole. The rotor portion should be electroneutral overall with large charges preferably located as far as possible from the rotor axis. Preferably the rotor portion is mechanically balanced, with its rotational axis approximately coincident with one of the axes of inertia. The substituents on the wing tips may be polar or charged to provide the rotor portion with a dipole moment. Other rotor portions with a dipole moment may be used, as desired. The rotor may be as simple as mono-, or di-chloromethyl group. Useful substituents are known in the art, such as SO3xe2x88x92, N+Me3, and others.
The length of the axle may be chosen as desired. Preferably the axle is long enough to prevent the blades of the rotor portion of the dipolar rotor from contacting the surface while rotating.
General structures of dipolar rotors are those shown below: 
where X is the base, the single bond, triple bond or metal (M) such as a transition metal form the axle and Y is the rotor. The circle represents a ring structure, for example, a four or five or six membered aromatic or nonaromatic ring with suitable substituents as shown and described herein, or various combinations of structures that perform the desired function.
Examples of small dipolar rotors are shown below: 
In 1 and 1A, three chlorine atoms are shown attached to silicon. When these structures are bonded to a surface such as glass, the chlorines react with hydroxyl groups on surface and Sixe2x80x94O bonds are formed, and the chlorines are leaving groups. In 1, Si is the base, the Sixe2x80x94C bond is the axle, and H2Cl is the rotor portion. In 1A, the acetylene bond is the axle. Another small dipolar rotors is shown below. 
The chlorines may be replaced with any halogen. Again, when the rotors shown above are attached to the surface, the ethyl groups may act as leaving groups. The chemistry of attaching molecules to surfaces is well known.
A larger dipolar rotor is shown below. 
In the structure shown above, the ring structure is the rotor portion.
The dipolar rotor may be constructed with various substituents. For example, the substituents on the aromatic ring in structure 3 may be changed. One example of changing substituents in 3 above would be to use substituents that contain positive or negative charges. These structures and substituents are known in the art.
Other more complicated structures are possible, as shown below: 
Even larger structures are possible, including those shown below: 
where M is a metal, preferably a transition metal, the Z""s are the xe2x80x9ctentaclesxe2x80x9d useful for bonding to a surface; and the Y""s and X""s form the rotor blades of the rotor portion. The Z""s may be the same or different. A simple Z is xe2x80x94Hgxe2x80x94Sxe2x80x94Zxe2x80x2, where Zxe2x80x2 is xe2x80x94(CH2)nSi(OR)3 where n is an integer from 0 to 15, preferably from 0 to 5 and R is an alkyl group, preferably a short alkyl group with from 1 to 5 carbons. X may be an aromatic ring with p-substituents that are polar or charged. Y may be a similar aromatic ring with opposing p-substituents. Other substituents for X and Y are well known in the art.
Other larger structures are shown below. 
In the structures shown herein, the following combinations of substituents may be used, for example:(1) Xxe2x95x90NO2, Yxe2x95x90NMe2, Txe2x95x90C; (2) Xxe2x95x90SO3xe2x88x92; Yxe2x95x90NMe3+, Txe2x95x90C; and (3) Xxe2x95x90CH3, Yxe2x95x90O, Txe2x95x90N.
Another large dipolar rotor is shown below: 
An example of replacing the base of structure 3 with a different base is shown below: 
where R is an alkyl group.
Other large dipolar rotors are shown below: 
FIG. 1 shows an example of a specific surface mounted molecular dipolar rotor.
Both single dipolar rotors and 2-dimensional arrays of interacting dipolar rotors are described.
Organic synthesis of the molecular dipolar rotors can be used to engineer all important properties. Properties such as the size and moment of inertia of the rotor portion, its height above the surface, the rotational friction, the magnitude of the dipole and the spacing of an array of dipoles, and thus ultimately its Curie temperature (the temperature at which ferromagnetism changes to paramagnetism), propagation velocities, dissipation, etc., can be controlled by design of the chemical structure and choice of base, axle, rotor and bearing elements making up the dipolar rotor and of the location of the dipolar rotors in the array (geometry of the array and inter-rotor distances).
The rotors may be driven to cause the dipole to move or oscillate. The rotors may be driven in a variety of ways, such as pendulum-type motion of the axle and rotor, or rotational motion of the rotor portion. The latter is preferred in many applications, because it has no characteristic frequency. The rotors may be driven in a variety of ways, such as electrically, magnetically, mechanically or optically. Driving the rotor with an alternating electric field induces detectable current in nearby electrodes. Even a single two-dimensional layer of dipolar rotors contains sufficient polarization density to be useful in electronic devices.
Methods of synthesis of dipolar rotors are determined by one of ordinary skill in the art without undue experimentation. In addition to the synthesis and construction methods described herein, other synthesis and construction methods are described in U.S. Pat. No. 5,876,830 (issued Mar. 2, 1999 to Michl et al.), hereby incorporated by reference to the extent not inconsistent with the disclosure herein. Methods of using the dipolar rotors are described herein, or easily determined by one of ordinary skill in the art without undue experimentation.